Methods and Apparatuses for Vertebral Body Distraction and Fusion Employing a Coaxial Screw Gear Sleeve Mechanism

ABSTRACT

Medical devices in accordance with various embodiments of the present invention employ one or more coaxial screw gear sleeve mechanisms. In various embodiments, coaxial screw gear sleeve mechanisms include a post with a threaded exterior surface and a corresponding sleeve configured to surround the post, the corresponding sleeve having a threaded interior surface configured to interface with the threaded exterior surface of the post and a geared exterior surface. A drive mechanism can be configured to interface with the geared exterior surface of the sleeve, causing the device to expand.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/591,463, filed Aug. 22, 2012, which is a continuation of U.S.application Ser. No. 12/841,465 filed Jul. 22, 2010, which claims thebenefit of U.S. Provisional Application No. 61/271,548 filed Jul. 22,2009 and U.S. Provisional Application No. 61/365,131, filed Jul. 16,2010, which are hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the distraction and fusion of vertebralbodies. More specifically, the present invention relates to devices andassociated methods for distraction and fusion of vertebral bodies thatutilize coaxial screw gear sleeve mechanisms.

BACKGROUND OF THE INVENTION

The concept of intervertebral fusion for the cervical and lumbar spinefollowing a discectomy was generally introduced in the 1960s. Itinvolved coring out a bone graft from the hip and implanting the graftinto the disc space. The disc space was prepared by coring out the spaceto match the implant. The advantages of this concept were that itprovided a large surface area of bone to bone contact and placed thegraft under loading forces that allowed osteoconduction and inductionenhancing bone fusion. However, the technique is seldom practiced todaydue to numerous disadvantages including lengthy operation time,destruction of a large portion of the disc space, high risk of nerveinjury, and hip pain after harvesting the bone graft.

Presently, at least two devices are commonly used to perform theintervertebral portion of an intervertebral body fusion: the first isthe distraction device and the second is the intervertebral body fusiondevice, often referred to as a cage. Cages can be implanted asstandalone devices or as part of a circumferential fusion approach withpedicle screws and rods. The concept is to introduce an implant thatwill distract a collapsed disc and decompress the nerve root, allow loadsharing to enhance bone formation and to implant a device that is smallenough to allow implantation with minimal retraction and pulling onnerves.

In a typical intervertebral body fusion procedure, a portion of theintervertebral disc is first removed from between the vertebral bodies.This can be done through either a direct open approach or a minimallyinvasive approach. Disc shavers, pituitary rongeours, curettes, and/ordisc scrapers can be used to remove the nucleus and a portion of eitherthe anterior or posterior annulus to allow implantation and access tothe inner disc space. The distraction device is inserted into thecleared space to enlarge the disc space and the vertebral bodies areseparated by actuating the distraction device. Enlarging the disc spaceis important because it also opens the foramen where the nerve rootexists. It is important that during the distraction process one does notover-distract the facet joints. An intervertebral fusion device is nextinserted into the distracted space and bone growth factor, such asautograft, a collagen sponge with bone morphogenetic protein, or otherbone enhancing substance may be inserted, either before or afterinsertion of the device into the disc space, into the space within theintervertebral fusion device to promote the fusion of the vertebralbodies.

Intervertebral fusion and distraction can be performed through anterior,posterior, oblique, and lateral approaches. Each approach has its ownanatomic challenges, but the general concept is to fuse adjacentvertebra in the cervical thoracic or lumbar spine. Devices have beenmade from various materials. Such materials include cadaveric cancellousbone, carbon fiber, titanium and polyetheretherketone (PEEK). Deviceshave also been made into different shapes such as a bean shape, footballshape, banana shape, wedge shape and a threaded cylindrical cage.

It is important for a device that is utilized for both intervertebralbody fusion and distraction to be both small enough to facilitateinsertion into the intervertebral space and of sufficient height tomaintain the normal height of the disc space. Use of an undersizeddevice that cannot expand to a sufficient height can result ininadequate fusion between the adjacent vertebrae and lead to furthercomplications for the patient, such as migration of the device within orextrusion out of the disc space. Addressing these issues can require theuse of multiple devices of varying sizes to be used serially to expandthe disc space the proper amount, which increases the time required tocarry out the procedure, increasing the cost and risk associated withthe procedure.

Accordingly, there is a need in the art for a device of sufficientstrength that can distract from a beginning size small enough toinitially fit into the disc space to a height sufficient to reestablishand maintain the normal height of the disc space.

SUMMARY OF THE INVENTION

Improved methods and apparatuses for vertebral body distraction andfusion in accordance with various embodiments of the present inventionemploy one or more coaxial screw gear sleeve mechanisms. In variousembodiments, coaxial screw gear sleeve mechanisms includes a post with athreaded exterior surface and a corresponding sleeve configured tosurround the post, the corresponding sleeve having a threaded interiorsurface configured to interface with the threaded exterior surface ofthe post and a geared exterior surface. A drive mechanism can beconfigured to interface with the geared exterior surface of the sleeve,causing the device to distract.

In one embodiment, a device is used for both intervertebral distractionand fusion of an intervertebral disc space. The device can include afirst bearing surface and a second bearing surface with at least onecoaxial screw gear sleeve mechanism disposed in between. The coaxialscrew gear sleeve mechanism includes a post with a threaded exteriorsurface projecting inwardly from one of the bearing surfaces and acorresponding sleeve configured to surround the post. The sleeve canproject inwardly from the other of the bearing surfaces and have athreaded interior surface configured to interface with the threadedexterior surface of the post and a geared exterior surface. The devicecan further include a drive mechanism having a surface configured tointerface with and drive the geared exterior surface of the sleeve,which causes a distraction of the first bearing surface and the secondbearing surface.

In another embodiment, a method of intervertebral body distraction andfusion involves implantation of a distractible intervertebral bodyfusion device into an intervertebral disc space. The device is insertedsuch that a first bearing surface interfaces with an end plate of asuperior vertebra of the intervertebral disc space and a second bearingsurface interfaces with an end plate of an inferior vertebra of the discspace. At least one coaxial screw gear sleeve mechanism is disposedbetween the bearing surfaces and includes a threaded post, acorresponding sleeve having an interior thread mating with the threadedpost and an exterior gear mating with a drive mechanism. The methodincludes distracting the device from a collapsed configuration to anexpanded configuration by operating the drive mechanism to rotate thesleeve relative to the post, thereby expanding the first bearing surfacewith respect to the second bearing surface.

The above summary of the various embodiments of the invention is notintended to describe each illustrated embodiment or every implementationof the invention. This summary represents a simplified overview ofcertain aspects of the invention to facilitate a basic understanding ofthe invention and is not intended to identify key or critical elementsof the invention or delineate the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1A is perspective view of a distractible intervertebral body fusiondevice according to an embodiment of the present invention in acollapsed configuration.

FIG. 1B is a perspective view of the distractible intervertebral bodyfusion device of FIG. 1A in an expanded configuration.

FIG. 1C is an exploded view of the distractible intervertebral bodyfusion device of FIG. 1A.

FIG. 1D is a partial sectional view of the distractible intervertebralbody fusion device of FIG. 1A.

FIG. 2A is a partial side view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 2B is a partial side view of the distractible intervertebral bodyfusion device of FIG. 2A.

FIG. 3A is a partial side view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 3B is a partial side view of the distractible intervertebral bodyfusion device of FIG. 3A.

FIG. 4A is a partial top view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 4B is a partial top view of the distractible intervertebral bodyfusion device of FIG. 4A.

FIG. 5A is a perspective view of an insertion tool and a distractibleintervertebral body fusion device according to an embodiment of thepresent invention.

FIG. 5B is a perspective view of an insertion tool and a distractibleintervertebral body fusion device according to an embodiment of thepresent invention.

FIG. 5C is a perspective view of an insertion tool and a distractibleintervertebral body fusion device according to an embodiment of thepresent invention.

FIG. 5D is a partial perspective view of an insertion tool according toan embodiment of the present invention.

FIG. 6A is an end view of a distractible intervertebral body fusiondevice according to an embodiment of the present invention.

FIG. 6B is a cross-sectional end view of the distractible intervertebralbody fusion device of FIG. 6A taken looking into the page.

FIG. 7A is a front view of a distractible intervertebral body fusiondevice according to an embodiment of the present invention.

FIG. 7B is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 7A taken along the lines 7B-7B.

FIG. 8A is a front view of a distractible intervertebral body fusiondevice according to an embodiment of the present invention.

FIG. 8B is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 8A taken along the lines 8A-8A.

FIG. 9A is an exploded view of a distractible intervertebral body fusiondevice according to an embodiment of the present invention.

FIG. 9B is a perspective view of the distractible intervertebral bodyfusion device of FIG. 9A.

FIG. 9C is a front view of the distractible intervertebral body fusiondevice of FIG. 9A.

FIG. 9D is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 9A taken along the lines 9D-9D in FIG. 9C.

FIG. 10A is an exploded view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 10B is a perspective view of the distractible intervertebral bodyfusion device of FIG. 10A.

FIG. 10C is a bottom view of the distractible intervertebral body fusiondevice of FIG. 10A.

FIG. 10D is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 10A taken along the lines 10D-10D in FIG.10C.

FIG. 11A is a perspective view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 11B is a front view of the distractible intervertebral body fusiondevice of FIG. 11A.

FIG. 11C is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 11A taken along the lines 11C-11C in FIG.11B.

FIG. 11D is a cross-sectional view of the distractible intervertebralbody fusion device of FIG. 11A taken along the lines 11D-11D in FIG.11B.

FIG. 12A is a perspective view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 12B is a side view of the distractible intervertebral body fusiondevice of FIG. 12A.

FIG. 13A is a perspective view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 13B is a side view of the distractible intervertebral body fusiondevice of FIG. 13A.

FIG. 14A is a perspective view of a distractible intervertebral bodyfusion device according to an embodiment of the present invention.

FIG. 14B is a side view of the distractible intervertebral body fusiondevice of FIG. 14A.

FIG. 15 is a perspective view of a pair of distractible intervertebralbody fusion devices according to an embodiment of the present invention.

FIG. 16A is a top view of a distractible device according to anembodiment of the present invention in a compressed configuration.

FIG. 16B is a top view of the distractible device of FIG. 16A in anexpanded configuration.

FIG. 17A is perspective view of a distractible device according to anembodiment of the present invention.

FIG. 17B is a partial cutaway view of the distractible device of FIG.17A.

FIG. 18A is a perspective view of a distractible device according to anembodiment of the present invention.

FIG. 18B is a partial view of the distractible device according of FIG.18A.

FIG. 18C is a partial view of the distractible device according of FIG.18A.

FIG. 18D is a partial view of the distractible device according of FIG.18A.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, one skilled in the artwill recognize that the present invention may be practiced without thesespecific details. In other instances, well-known methods, procedures,and components have not been described in detail so as to notunnecessarily obscure aspects of the present invention.

Referring to FIGS. 1A-1C, there can be seen a distractibleintervertebral body fusion device 100 adapted for implantation into anintervertebral disc space of a patient according to an embodiment of thepresent invention. FIG. 1A shows the device 100 in a fully compressedconfiguration, FIG. 1B shows the device 100 in a fully expandedconfiguration, and FIG. 1C shows an exploded view of the device 100.

Device 100 includes a first member 110 having a bearing surface 102configured to interface with an end plate of one of a superior or aninferior vertebra of the intervertebral disc space and a second member150 having a bearing surface 104 configured to interface with an endplate of the other of the superior or inferior vertebra. In oneembodiment, the bearing surfaces 102, 104 can include a texturedsurface, such as that provided by corrugations 114, to create frictionwith the end plates of the vertebra to prevent accidental extrusion ofthe device 100. The radii of the corrugation 114 valley and thecorrugation 114 top width can be maximized to minimize the notch factorand reduce stress while still providing a corrugation design thatreduces the propensity of the device 100 to extrude from the disc space.One or both of the members 110, 150, can also include an opening 173,153 extending through the member for facilitating bone growth throughthe device 100. In other embodiments, opening can be filled with a gel,rubber, or other complaint material that can replicate the nucleus of anintervertebral disc and supplement the strength of the device incompressive, shear, and torsional loading conditions. Alternatively, agenerally solid surface, a textured or etched surface, a scored ornotched surface, or a surface with multiple openings can be provided oneach member 110, 150.

Device 100 can also include a pair of coaxial screw gear sleevemechanisms including threaded post members 111, 112 extending from firstmember 110 and a pair of threaded geared sleeves 120, 130 configured tosurround the post members 111, 112. Threaded post members 111, 112 canhave threads 113, 115 defined on an exterior surface thereof. Threadedgeared sleeves 120, 130 can have both interior threads 122, 132configured to interface with the threads 113, 115 of threaded postmembers 111, 112 and exterior threads 121, 131. In one embodiment, boththe exterior 121 and interior 122 threads of one of the sleeves 120 areof an opposite hand to the threads 131, 132 of the other sleeve 130.External threads 121, 131 of sleeves 120, 130 can have gear teeth 124,134 cut into the thread. In one embodiment, the gear teeth 124, 134 arenot cut down to the root, or minor diameter, of the threads 121, 131 inorder to maximize the strength of the threads. In the compressedconfiguration, threaded geared sleeves 120, 130 can fit within sleeveopenings of 161, 162 in second member 150. Openings 161, 162 can includethreaded portions 151, 152 that mesh with exterior threads 121, 131 ofthreaded geared sleeves 120, 130. In one embodiment, sleeve openings161, 162 extend all the way through bearing surface 104 of second member150. In some embodiments, as pictured, threaded geared sleeves 120, 130can be substantially solid. In other embodiments, threaded gearedsleeves can include one or more slots through the sleeve for massreduction and material savings or to promote bone in-growth.

The device 100 can be expanded with the aid of a worm 140 that extendsthrough a worm aperture 154 in the device 100. The worm 140 can havefirst 142 and second 141 opposing threaded sections configured tointerface with the exterior threads having gear teeth 124, 134 ofthreaded geared sleeves 120, 130 through a pair of apertures 157, 158 inthreaded portions 151, 152 of sleeve openings 161, 162. The worm 140 caninclude a hex 143, 144 at each end of the worm 140 that allows it to bedriven by a delivery system (described below). Such a delivery systemcan also be attached to the device 100 when driving the worm 140 attapped hole 156A or tapped hole 156B to stabilize the delivery system.Device 100 can include a hex 143, 144 and tapped hole 156A, 156B at eachend of device, so that the device 100 can be inserted and driven fromeither end, or can include a hex and tapped hole at only one side of thedevice, limiting the device to insertion and distraction from a singledirection. Bottom member 150 can also include one or more scallops 155above the worm aperture 154 that provide increased strength andthickness while still allowing the threaded geared sleeves 120, 130 torotate.

A partial sectional view of a distractible intervertebral body fusiondevice 100 in FIG. 1D, helps illustrate how the device can employmultiple coaxial screw gear sleeve mechanisms as telescoping mechanismsutilizing the threaded post members 111, 112, threaded geared sleeves120, 130 and the worm 140 to expand the first member 110 and secondmember 150 relative to each other. By turning hex 144 counterclockwise,and therefore the worm 140 counterclockwise, first threaded section 142of worm 140 pulls the gear teeth 134 of threaded geared sleeve 130towards the hex head 144. This causes the sleeve 130 to translate upwardfrom the second member 150 along internal threads 152. As the sleeve 130rotates while it translates upward, the threaded post member 112extending from the first member 110, which is unable to turn, alsotranslates upward with respect to the sleeve 130 and the second member150. This second translation results from the opposite handed externalthreads 115 of the threaded post member 112 being driven by the matchinginternal threads 132 of the sleeve 130. The same mechanics are occurringon the other side of the device with oppositely threaded sleeve 120having external threads 121 and internal threads 122, post member 111having external threads 113 and second threaded section 141 of worm 140.

Because the threads for like components for each device are oppositehanded, the threads 142 on one side of the worm 140 will be pulling thegear teeth 134 of the threaded geared sleeve 130 while the threads 141on the other side of the worm 140 will be pushing the gear teeth 124 onthe other sleeve 120, or vice versa depending on the direction ofrotation of the worm 140. These opposing forces applied to the worm 140by the threaded geared sleeves 120, 130 are carried in either tension orcompression by the worm 140. Therefore, the worm 140 is notsubstantially driven into or out of the worm aperture 154 as the device100 is expanded or contracted. This is advantageous in that a pin orother retainer is not required to retain the worm and balance the forcesin the device. Such a pin can be a point of excessive wear which cancause the life cycle of the device to be shorter lived. In someembodiments, a pin can be employed to prevent the worm 140 from beingable to be pulled or pushed axially, which can cause the device tobecome jammed.

Alternative drive mechanisms to worm drive include piezoelectricactuators and any momentum imparting collision mechanism orconfiguration. Additionally, a drive mechanism, such as a worm, could bean integrated part of a delivery system. In such an embodiment, theexternal threads of the threaded geared sleeves would both be of thesame hand and the worm would be screwed into the compressed device inthe worm aperture. As the worm is turned, the axial position of the wormwould be constrained by the delivery system, instead of a pin, resultingin distraction of the device. Once the device reached the desiredheight, the worm could be screwed out of the worm aperture and thedevice could be locked in place by screwing in a threaded locking worm.The locking worm could have an additional threaded or snapping featurethat enables it to be permanently, or in a removable fashion, attachedto the device. The locking worm could be made from a radio transparentmaterial such as PEEK, which would therefore allow imaging through theworm. The locking worm would only need to be strong enough to inhibitthe threaded geared sleeves from turning into or out of the device, andwould not need to be strong enough to cause the device to distract. Alarger radio transparent window could be formed by removing a portion ofthe sides of the bottom member on either side of the opening in thebottom member along the length of the device, so long as the deviceretained a necessary amount of stiffness.

Referring now to FIGS. 2A and 2B, a preferred fit of gear teeth 124, 134of threaded geared sleeves 120, 130 in internal threaded portions, 151,152 of second member 150 is shown. As the gear teeth 124, 134 are thrusttowards the internal threads 151, 152 of the second member 150 by theworm, the load between the gear teeth 124, 134 and threads 151, 152 isbalanced by the bearing surfaces 163, 164 between the components, whichresults in the ability of the device 100 to distract a substantial load.This fit between the gear teeth 124, 134 and the internal threads 151,152 can be contrast with the fit shown in FIGS. 3A and 3B. In thosefigures, when the gear teeth 124′, 134′ of the threaded geared sleeves120′, 130′ are thrust towards the internal threads 151′, 152′ of thesecond member 150′, the force is not balanced by bearing surfaces as inFIG. 2B, but by the force the internal threads 151′, 152′ apply to thegear teeth 124′, 134′. This can result in the gear teeth 124′, 134′acting as a wedge and becoming jammed against the internal threads 151′,152′, which dramatically reduces the ability of the device to distractsubstantial loads and makes the device more sensitive to frictionbetween components. Optionally, a liquid or gas lubricant, such assilicon lubricant, may be used to reduce friction in the mechanism.Saline may also be used as a lubricant.

It should be noted that although the threads depicted in the Figures areall screw threads in the form of projecting helical ribs, “thread” forthe purposes of the present invention can also refer to any othermechanism that translates rotational force into translational orlongitudinal movement. For example, in some embodiments threads can becomprised of a recirculating or spiral arrangement of bearings or anyother low friction arrangement, such as cooperating magnets.

In one embodiment, the height of the device 100 between the bearingsurfaces 102, 104 in the fully compressed configuration is 6.5millimeters and the maximum fully distracted height is 12 millimeters,thus providing a very large amount of distraction relative to theinitial height of the device. The maximum height is defined by thelargest height at which the device can meet the dynamic compressive,shear, and torsional requirements for implantable intervertebral bodyfusion devices. Variables that determine this height include the widthof the threaded geared sleeves, which is limited by the desired width ofthe device, and the material from which the device is made. With regardto the material for the device, materials with higher fatigueperformance allow the maximum height of the device to be taller evenwith a narrower width. In one embodiment, the device is made fromtitanium. The device may also be made from cobalt chrome, MP35N, orPEEK, for increased strength characteristics or increased radiolucentcharacteristics, depending on the material. X-ray transparency is adesirable property because it allows for the fusing bone to be imagedthrough the device. In one embodiment, the device can be designed suchthat in the compressed configuration the threaded geared sleeves projectthrough the bearing surface of second member in order to provide for aneven greater amount of distraction. To accommodate the device onimplantation, openings configured to contain the projecting portions ofthe sleeves can be cut into the adjacent vertebral end plate.

Once distracted, device 100 does not require a locking mechanism tomaintain the desired height within the body. This is because, whendriven backwards, the device exhibits a very high gear ratio whichcauses even the slightest friction in the system to overwhelm any amountof compression, torsion, or shear loading that might be applied to thedevice. In dynamic testing in shear, torsion, and compression, themaximum amount by which the height of the device changed was byapproximately 0.01 millimeter. The device 100, because height can bemaintained at any point along the threaded geared sleeves, thereforealso exhibits very high resolution height control, on the order of 1micrometer.

In one embodiment, the external threads 121, 131 and gear teeth 124, 134on the threaded geared sleeves 120, 130 can be substantially trapezoidalin shape. In one embodiment, the thread is a trapezoidal 8 millimeter by1.5 millimeter metric thread. A trapezoidal design enables a relativelylarge gear tooth size and, accordingly, a larger area over which thedistraction loading is distributed. Additionally, with precisemanufacturing, multiple gear teeth 124, 134 on the threaded gearedsleeves 120, 130 can be engaged by the worm 140 at the same time alongthe pressure angle ANG, as shown in FIGS. 4A and 4B. Distributing thedistraction load over multiple teeth of the sleeves 120, 130 and theworm 140 is critical to achieve the minimum device size while providinga maximum amount of distraction and load capacity.

A delivery system 200 for implanting a distractible intervertebral bodyfusion device according to an embodiment of the present invention isdepicted in FIGS. 5A (compressed configuration), 5B (partiallydistracted configuration, and 5C (fully distracted configuration).Delivery system 200 also includes an actuation tool 300 for actuatingthe distraction.

To distract the device 100, a hex 143 or 144 of device is firstconnected to the delivery system 200 via a socket driver on an end 201of delivery shaft 203. In order to more securely attach the device 100and the delivery system 200, a threaded end 202 of delivery shaft 204can be threaded into one of tapped holes 156A or 156B in second member150 of device 100. The device 100 can then be inserted into the body viaa standard transforaminal lumbar interbody fusion (TLIF) or posteriorlumbar interbody fusion (PLIF) procedure using the delivery system 200.A lateral interbody fusion through the lateral retroperitoneal corridoris another approach. The delivery system 200 can guide the location ofthe device 100 as it is being inserted with use of handle 213.

Delivery system 200 includes a hex 215 and a circumferential groove 214at the near end of delivery shaft 204, and also has a hex andcircumferential groove (not pictured) at the end of delivery shaft 203.Once the device 100 is in the disc space, the actuation tool 300 can beconnected to the delivery system by engaging an internal hex socketdriver of the actuation tool with the hex on the end of the deliveryshaft 203, 204. In some embodiments, an internal snap ring orcircumferential spring in actuation tool 300 can engage thecircumferential groove on delivery shaft 203 to ensure that theactuation tool 300 does not become accidentally disengaged during use.

By turning the actuation tool 300, the user transmits torque down thedelivery shaft 203 to the worm 140, which distracts the device 100. Asthe delivery shaft 203 is turned, a slider 206 advances along threads209 on shaft 203. The height of the device 100 as it is expanded can berepresented on the delivery system 200 by the position of the slider 206along the delivery shaft 204 with fiducial marks 208, as shown best inFIG. 5D. Marks 208 may be positioned at any desirable interval alongdelivery shaft 204, and the slider 206 may include a viewing slot 207for more complete viewing of the marks 208 as they are reached by slider206. In one embodiment, each mark 208 can represent a distracted heightof 1 millimeter.

Delivery system 200 can be configured so that when the device 100reaches its maximum desired height, slider 206 abuts stop 205 so that itcan be advanced no further, thus limiting the height of the device 100.By allowing the delivery system 200 to limit the expansion, any damagedue to excessive torque is immediately apparent in the delivery system200, so no damage is sustained by the device 100. In another embodiment,the device 100 can limit its own expansion by welding two of the gearteeth 124, 134 on one of the threaded geared sleeves 120, 130 togetherso that they bind with the worm 140 when the device 100 has reached itsmaximum desired height. Similarly, in other embodiments, one or more ofthe gear teeth 124, 134 can be omitted or a small post can be insertedinto the interstitial space between two gear teeth to limit theexpansion of the device.

In one embodiment, a lever for applying torque to the shaft 204 may beaffixed to the hex 215 at the end of shaft 204. The lever may be shapedand oriented such that when the device 100 is appropriately engaged withthe delivery system 200, the position of the lever allows access to thedrive shaft 203, whereas when the device is not appropriately engaged,the lever does not allow access to the drive shaft 203. In anotherembodiment, the slider 206 may be contained with the handle 213 in orderto reduce the length of the delivery system 200. In another embodiment,a tube able to carry loading in torsion may be implemented around one ofthe shafts 203, 204 to add to the structural rigidity of the deliverysystem. A small foot may be affixed to the tube to additionally supportthe ability of the delivery system to carry, and transmit, loading intorsion by and to the device. In another embodiment, the shaft of thedelivery system 200 can be curved or bayonet in shape to allowvisualization through a minimally invasive system and working channel.

The actuation tool 300 can include a recess or loop 304 that allows thatuser to spin the actuation tool 300 with a single finger and/or largegripping surfaces 301 that the user can grasp to turn the actuation tool300. In one embodiment, the loop may be lined with a slippery or bearingsurface to enable the loop to spin easily around the user's glovedfinger(s). The actuation tool 300 can also include a broad surface 303designed to receive the impact of a hammer for implantation. Recesses302 can also be included on actuation tool 300 to afford the user animproved view of the device 100 while it is being implanted. Actuationtool 300 can span both delivery shafts 203, 204 and may extend overand/or receive handle 213 of delivery system 200. In another embodiment,rather than being driven by manual actuation tool 300, the device 100can be driven by a powered actuation implement such as a pneumatic orelectric drill or a motorized screwdriver mechanism, which, in someembodiments, can allow the tool to be controlled remotely.

In other embodiments, the actuation tool, manual or automatic, employssensors in the device to transmit data regarding the implantationparameters and environment, such as device load and muscular tension, toan operator or operating system to improve the performance of thesurgical procedure and outcome. The delivery system 200 could use smallstrain gauges located on the device 100 and/or load cells attached tothe delivery shafts 203, 204 and actuation tool to measure loads presentduring the implantation and distraction process. These gauges and/orload cells could be monitored by a microcontroller board located on thedelivery system 200 and the information fed back to a monitoringcomputer via a standard interface such as a USB or wireless connection.This information could be used to closely monitor a procedure'sprogress, warn of impending problems and improve future procedures. Ifnot fully bridged, the gauges could be configured as half bridges withinthe device and completed outside of the device. Standard signalconditioning amplifiers could be used to excite and condition the signalto yield a measurable output of voltage and current.

In one embodiment, the device 100 can have a strengthened second member150 as shown in FIGS. 6A and 6B. This can be done by lowering the wormaperture 154, and therefore the worm 140, such that when the device 100is expanded to its full height, the worm 140 engages a full gear tooth134A on the threaded geared sleeve 130 closest to the bottom 136 of thethreaded geared sleeve 130. This allows a top surface 166 of the secondmember 150 to be lowered, which allows the first member 110 to bethicker, and therefore stronger, while maintain the same initial heightIn addition, this allows the material 168 between the top surface 166 ofthe second member 150 and the worm aperture 154 to be made thicker. Afurther advantage of this configuration is that at least one fullinternal thread 152A of the second member 150 is in engagement with thethreaded geared sleeve 134 when the device is fully distracted. In sucha configuration, an additional thickness 167 can be added to the side ofsecond member 150 opposite of the worm aperture 154 to what waspreviously described as the top surface 166A of that side of the secondmember 150. This allows for a full internal thread 152B to engage thethreaded geared sleeve 130 on the side opposite of internal thread 152A.By capturing the threaded geared sleeve with a full thread on bothsides, when the device is loaded with shear and torsion, a maximumamount of material is resisting the load, which minimizes the resultingstress and increases the fatigue life of the device 100.

FIGS. 7A and 7B depict another embodiment of the present invention wherein threaded posts 111, 112 employ a buttress thread 113A, 115A (comparethreads 113A in FIG. 7B to threads 113, 115 in FIG. 1D). A buttressthread configuration results in the load bearing thread face beingperpendicular to the screw axis of the post 111, 112, which increasesthe axial strength of the device. FIGS. 8A and 8B depict a furtherembodiment that utilizes a standard 60 degree thread 113B, 115B onthreaded posts 111, 112. 60 degree threads are considered industrystandard and can therefore be created with common machining practices.This can result in a device that can be more quickly and inexpensivelyproduced.

Referring now to FIGS. 9A-9D, another embodiment of a distractibleintervertebral body fusion device 400 includes a single pair of threadedgeared posts 423 extending between first member 410 and second member450 rather than the separate threaded geared sleeves 120, 130 andthreaded posts 111,112 described previously. Threaded geared posts 423each include a threaded geared portion 421 and a post portion 411.Threaded geared portions 421 fit within openings 461 in second member450 and interface with worm 440 and internal threads 451 to cause thedevice 400 to distract. Post portions 411 fit within openings 416 infirst member 410 and can be attached to washers 418. Washers 418 keepthe first member 410 in place relative to the threaded geared posts 423as the threaded geared posts 423 rotate freely independent of the firstmember 410 when the device 400 is actuated. Thus, as seen in FIGS. 9Cand 9D, the distraction between the first member 410 and the secondmember 450 is caused by the thicker threaded geared portions 421 whilethe post portions 411 remain within the openings 416 in first member410. This leads to a device 400 having increased axial strength.

FIGS. 10A-10D depict a further embodiment of a distractibleintervertebral body fusion device 500 that allows for differentialadjustment of the threaded geared sleeves 520. Threaded posts 511 caneach include an arched portion 515 that corresponds to an arched recess517 in first member 510. The arched interface between the threaded posts511 and the first member 510 created by the corresponding archedportions 515 and arched recesses 517 allows the first member 510 torotate and become angled relative to the second member 550. A pin jointutilizing a pivot pin 572 can be used to keep one interface between thefirst member 510 and a threaded post 511 stationary, while the otherinterface is allowed to slide due to the arched surfaces. A placementpin 570 is used to prevent the worm 540 from sliding out of the secondmember 550 when distracting the device. Worm 540 can be a two-part wormincluding a first portion 546 having a first threaded section 543 andsecond portion 548 having a second threaded section 544 that fits onto apost 547 of first portion 546. The two portions 546, 548 can thereforebe rotated independently of each other, with each driving a separatethreaded geared sleeve 520. Because each threaded geared sleeve 520 canbe engaged separately, they can be distracted different amounts,resulting in an angled first member 510 as shown most clearly in FIG.10D. Such a configuration accommodates lordotic or kyphotic geometry.Optionally, the arched recesses 517 in the first member 550 and archedsurfaces 515 of the posts 511 could be replaced with flexural joints orball or cylinder and socket joints.

A distractible intervertebral body fusion device 600 according toanother embodiment of the present invention is depicted in FIGS.11A-11D. Device 600 uses three coaxial screw gear sleeve mechanisms,each having a threaded geared sleeve 620 and a threaded post 621,between first member 610 and second member 650. As seen in FIGS. 11C and11D, to distract the device, the worm drive 640 is rotated and itengages one of the threaded geared sleeves 620, causing it to rotate. Asthe first threaded geared sleeve 620 rotates, it engages the other twothreaded geared sleeves 620, causing them to rotate and the device 600to distract. The rotation of the threaded geared sleeves 620 also causesthe threaded posts 621 to distract, as described previously. Use ofthree coaxial screw gear sleeve mechanisms provides for a device havingincreased strength in the axial direction, a broader surface area forsupporting the endplate of the vertebral body, and a more shapelygeometry. Optionally, each of the three distraction mechanisms could beactuated independently to adjust the surface of the device in additionaldegrees of freedom. To achieve some geometries, the drive mechanisms mayneed to be flexible, in which case a bellows or spiral laser-cut drivemechanism capable of bending and transmitting torque could beimplemented. More specifically, one such drive mechanism could wraparound many distraction mechanisms, and distract each one with only oneinput. In another embodiment, a flexible drive mechanism could be usefulin actuating multiple drive mechanisms separately to control the membersof the device in many spatial degrees.

FIGS. 12A and 12B depict a distractible intervertebral body fusiondevice 700 that employs only a single coaxial screw gear mechanismhaving a threaded geared sleeve 720 and a threaded post 721 fordistracting first member 710 relative to second member 750 with worm740. Device 700 also can include first 774 and second 776 telescopingsupport elements. Telescoping support elements 774, 776 serve tomaintain the relative rotational positioning of the first member 710with respect to the second member 750, enabling the threaded gearedsleeve 720 to rotate with respect to both the first member 710 andsecond member 750 to distract the device 700. FIGS. 13A and 13B depict afurther variation of device 700 that utilizes a plurality of spikes 778extending from the first member 710 and second member 750 torotationally constrain the first member 710 and second member 750. Inoperation, the spikes 778 contact the adjacent vertebral end plates andfix themselves to the end plates to prevent the first member 710 andsecond member 750 from rotating relative to each other. A furtherembodiment is depicted in FIGS. 14A and 14B. This embodiment includesonly a threaded geared sleeve 720 between first member 710 and secondmember 750 and allows the first member 710 to rotate with the sleeve 720as the device 700 is distracted via rotation of the worm 740.Optionally, first member 710 could be rotationally free with respect tothe threaded geared sleeve 720 so that the first member 710 is allowedto engage and not rotate against the endplate of the vertebral body.

In one embodiment, distractible intervertebral body fusion devices asdescribed herein can be made of titanium and the delivery system can bemade primarily out of stainless steel. Components of each mechanism thatslide against each other can be made of different types of the generalmaterial. For example, the first member can be made from Ti 6Al 4Vstandard titanium, which has high smooth fatigue performance, while thethreaded geared sleeves can be made from Ti 6Al 4V ELI, which has highnotched fatigue performance. Such a combination results in eachcomponent being made out of a preferred material for its fatigue notchfactor while the overall mechanism implements different materials wherecomponents are slidably arranged.

In various embodiments, device is shaped to be ergonomic. Device canhave various shapes, such as, for example, rectangular, kidney, orfootball shaped. A kidney or football shaped device maximizes contactbetween the device and the vertebral bodies because the end plates ofvertebrae tend to be slightly concave. One or both ends of the devicemay also be tapered in order to facilitate insertion. This minimizes theamount of force needed to initially insert the device and separate thevertebral bodies. In addition, the device may be convex along both itslength and its width, or bi-convex. Device can be constructed in varioussizes depending on the type of vertebra and size of patient with whichit is being used.

Device can be manufactured in various ways with, in some embodiments,different components of the device can be manufactured in differentways. In one embodiment, thread milling can be implemented tomanufacture the various threads in device. Wire EDM can be utilized tomanufacture some or all of the holes and openings in the device.Assembly jigs and post processing steps can also be utilized to allowthe device to be manufactured to exacting standards.

In some embodiments, following distraction of the device, a bone growthstimulant, such as autograft, bone morphogenic protein, or boneenhancing material, may be delivered into device. In one embodiment,bone growth stimulant is delivered through a hollow chamber in insertiontool before insertion tool is disengaged from device. The devicesupports in-vivo loads during the time fusion occurs between thevertebral bodies.

In one embodiment, the surface of the device can be treated to minimizesurface roughness or to reduce pitting of the material within the body.A rough surface or pits can increase the stress on the device, which canresult in shortening of the fatigue life and/or reduce fatigue strength.In one embodiment, the surface can be treated with electro-polishing,both removing burrs from the edges of the device and finishing thesurface. In another embodiment, the surface can be left untreatedbecause a rough surface on the end plates helps prevent accidentalextrusion of the device. In one embodiment, the device can also becoated with a highly elastic, impermeable material to extend its fatiguelife. Specifically, the impermeable material would prevent the corrosiveproperties of blood from degrading the device. In another embodiment,the device can be comprised of a biocompatible material, so that nocoating is necessary. In a further embodiment, the device can be made ofa biodegradable material designed to degrade in the body at a selectedstage of the healing process, such as after bone fusion.

In various embodiments, devices as described herein can be used withvarious bone growth stimulants. In one embodiment, a 3D premineralizedsilk fibroin protein scaffold carrier can be carried on the surface ofor within the device to deliver a bone morphogenetic protein (BMP),which can optionally be combined with modified bone marrow stromal cells(bMSCs) to improve fusion. In other embodiments, a composite chitosan 3Dfiber mesh scaffold or a gelatin scaffold can be used. The device canalso utilize vascular endothelial growth factor (VEGF) by depositingimmobilized VEGF on titanium alloy substrates coated with thin adherentpolydopamine film to increase the attachment, viability andproliferation of human dermal cells to promote the development of bloodsupply to the fused bone through revascularization around the implant.In some embodiments, certain polymers such as biodegradable PLGA couldbe used to make a scaffold for VEGF to enhance neovascularization andbone regeneration. In some embodiments, VEGF can be used in conjunctionwith BMPs to inhibit the function of BMPs of promoting osteogenesis toallow the device to be continually adjusted over time. In variousembodiments, scaffolds on or around the device could be seeded with bonemarrow derived stem cells, dental pulp derived stem cells and adiposederived stem cells. Scaffolds can also be comprised of various materialsincluding polyester (e.g., polylactic acid-co-glycolic acid orpoly3-hydroxybuetyrate-co-3-hydorxyvalerate), silk (e.g., biomimetic,apatitie-coated porous biomaterial based on silk fibroin scaffolds),hydrogels such as polycaprolactone, polyepsilon-caprolactone/collagen(mPCL/Col) cospun with PEO or gelatin, mPCL/Col meshes with micron-sizedfibers, and mPCL/Col microfibers cosprayed with Heprasil, and poroustitanium and titanium alloys (such as a titanium-niobium-zirconiumalloy) functionalized by a variety of surface treatments, such as a VEGFor calcium phosphate coating.

In some embodiments, device can include structure adapted to retain bonewithin an interior of or adjacent to the implant. Such structure caninclude a micro-level matrix or scaffolding or kerfs, divots, or othersimilar features in the body of device. Bone may also be retainedthrough use of a porous material such that bone is retained in theinterstitial spaces of the material. Larger, extending features may alsobe implemented. Such features, such as a circumferential shroud, couldalso have the added function of stiffening the device in torsion.

In some embodiments, more than one distractible intervertebral bodyfusion device according to the present invention can be implanted intothe disc space. As shown in FIG. 15, in one embodiment a pair of devices100 can be implanted such that the outer surface 104 of the secondmember 150 of one of the devices 100 directly interfaces with the outersurface 102 of the first member 110 of the other device 100. Such aconfiguration can allow for use of a smaller access channel forimplanting the devices. In one embodiment, the cooperating surfaces 102,104 of the two devices are flat. Devices 100 can be actuatedsimultaneously or separately. Devices could also be flipped with respectto each other in order to have both drive mechanisms centrally located.In addition, the devices could be configured to rotate or flex withrespect to each other to allow for the bearing surfaces of the devicesto adjust their position to comfortably engage with the endplates of thevertebral bodies, or to preserve motion of the spine.

In one embodiment, a rod and screws can be used with the device as partof an assembly affixed to the vertebral body. Specifically, posteriorfixation, whereby rod(s) and screws are used to supplement the spine,may be used in combination with the device. In one embodiment, therod(s) and screws may be affixed to, or designed to engage, the implant.In another embodiment, the members of the device may be extended and,effectively, folded over the sides of the adjacent vertebral bodies sothat the device may be affixed to the vertebral bodies with screwsplaced through the extensions of the members of the device substantiallyparallel to the plane formed by the endplates of the vertebral bodies.In other embodiments, an adhesive, which may support osteogenesis, maybe used to adhere the device to or within the spine.

In another embodiment distractible intervertebral body fusion device cancomprise an endplate enhanced with flexures to be capable of tiltingfront to back and/or side to side. Additionally, coaxial screw gearsleeve mechanisms utilizing at least in part a flexible material can beoriented around the periphery of the device to allow for tilting in avariety of axes. Generally, a device capable of tilting can bebeneficial in that providing additional degrees of flexibility builtinto the device can promote bone growth, distribute stress across thesurface of the end plates, and allow the device to adjust to thecurvature of an individual's spine.

In one embodiment, the device could be placed within a small sock-likeslip made from, for example, silk, which could be filled with bone. Asthe device expands and the volume of the device increases, the sockwould prevent the bone from falling out of the implant and/or allow formore bone to be introduced into the implant from the space around theimplant within the sock. Such a sock could be closeable at one end andcould attach to the delivery system during implantation of the device.The sock could be released from the delivery system during any of thelater steps of implantation.

A device in accordance with the various embodiments can be used for avariety of intervertebral fusion applications, including, for example,cervical, thoracic anterior lumbar, trans-foraminal lumbar, extremelateral lumbar, and posterior lumbar. Various embodiments ofimplantation procedures for these applications may be as follows:

Cervical: The device is implanted via an anterior approach at the C3 toC7 levels using autograft. The device is used with supplemental anteriorplate fixation.

Trans-foraminal lumbar: The device is implanted via a posterior approachfrom the L2 to S1 levels using autograft. The device is used withsupplemental posterior rod fixation.

Posterior lumbar: The device is implanted via a posterior approach fromthe L2 to 51 levels using autograft. Two devices are implanted; one onthe left side of the disc space and the other on the right side of thedisc space. The device is used with supplemental posterior rod fixation.

Anterior lumbar: The device is implanted via an anterior approach fromthe L3 to S1 levels using autograft. The device is used withsupplemental anterior plating fixation of posterior rod fixation.

Extreme lateral lumbar: The device is implanted via a lateral approachfrom the T12 to L4 levels using autograft. The device is used withsupplemental posterior rod fixation.

In another embodiment, the device can be used in vertebral bodyreplacement. After resection of a vertebral body or multiple vertebraedue to fracture or tumor, the device can be distracted to bridge twoseparate vertebrae. The distracted device bridges and supports the voidleft after resection. The device can be constructed in different sizesto accommodate the size difference of cervical, thoracic and lumbarvertebrae.

In another embodiment, the device can be used as an interspinousdistraction device as shown in FIGS. 16A and 16B. The device 800 can beplaced between two adjacent spinous processes 801 a, 801 b through aminimal access system. The device can be inserted in a collapsedconfiguration to allow ease of placement. Once in position, the devicecan be actuated to an expanded configuration with coaxial screw gearsleeve mechanisms 804 to lock the vertebrae in a distracted position.Coaxial screw gear sleeve mechanisms 804 can be configured as describedpreviously herein. The device can have gripping teeth 800 at the pointof contact with the spinous processes 801 a, 801 b to help fix it inplace.

In another embodiment, the device can be used for interspinous fusion.The device can be placed between two adjacent spinous processes througha minimal access system in a collapsed configuration. Once in position,the device can be actuated to lock the vertebra in a distractedposition. The device can have a bolt locking mechanism or similarlocking arrangement to lock the device in the distracted position and tolock the locking plates through the spinous processes. The device canalso have gripping corrugations or features on the outside to help keepit in place. Autograft or bone fusion enhancing material can be placedin the open space in device.

In another embodiment, the device can be used as a distractible fracturereducing device for osteoporotic bone. The device can be insertedbeneath an end plate fracture through a minimally invasive pedicleapproach. The device is then actuated with a delivery system actuator.Once the fracture is reduced, the device is explanted and the void isfilled with acrylic cement or another bone filler that will strengthenthe bone.

In another embodiment, the device can be used in facet jointreplacement. After resection of a hypertrophic facet joint, the devicecan be actuated. Each member can be fixed to adjacent vertebrae with apedicle screw. This will allow motion similar to that of a facet jointand prevent instability. The device can be part of a soft fusion devicesystem and can be used in combination with an intervertebral discreplacement device. The coaxial screw gear sleeve mechanism or threadedpost may also be used to make intervertebral disc replacement devicesexpandable.

In another embodiment, the device can be used as a programmabledistraction cage with a dynameter and bone stimulator. A programmablemicro-machine actuator device can be implanted within the device. Thedevice is distracted during implantation and can provide force readingsthrough a radio frequency communicator post-surgery. The shape of thedevice can be altered while it is implanted by distracting the memberswith the actuator device, which can result in lordosis, kyphosis,further distraction, or less distraction. In one embodiment, a batterydevice powers the system and can also form a magnetic field that worksas a bone stimulator. The battery life may be limited to a short periodof time, such as one week. Small movements of the device can be used togenerate electrical energy with piezo-electrics or conducting polymersthat may be used to recharge the batteries, capacitors, or other suchpower storage devices. Alternatively, the device may be powered throughan RF inductive or capacitatively coupled arrangement.

In another embodiment, the device can be a self-actuating distractiblecage. The device can be inserted into the disc space in a collapsedstate. Once the device is released, it can slowly distract to a presetheight.

In another embodiment, the device can be used in facial maxillarysurgery as a fracture lengthening device for mandibular fractures. Thedevice can be designed with narrow members having perpendicular plateswith holes that allow fixation of each member to either a proximal ordistal fracture. The device can be actuated to a preset height. Thiswill allow lengthening of the defect in cases of fracture bone loss,dysplasia, or hypoplasia.

In another embodiment, device can be used in orthopedic applications asa lengthening nail for distraction of long bone fractures. After anorthopedic fracture occurs with bone loss, a distractible elongatingnail can be placed to lengthen the bone. The elongation occurs over afew days with micrometer movements. This application will involve adistraction device inserted in between the moving portion of the nailsexerting counter-distraction forces, which will provide lengthening ofthe bone.

In another embodiment, the device can be used to replace phalangealjoints in the hand, metatarsal joints in the foot, or calcaneal-talusjoints. These joints can have implants that will allow motion ofadjacent bones and limit hyper-extension or hyper-flexion.

FIGS. 17A and 17B depict a distractible device 900 including anenveloping coaxial screw gear sleeve with recirculating bearingsaccording to another embodiment of the present invention. Device 900includes a post 910, an enveloping coaxial screw gear sleeve 920, a worm930 and a housing 940. Post 910 includes a smooth outer surface 912 anda machined helical raceway 911 for bearings 913. A helical raceway (notshown) is also machined into inner surface of enveloping coaxial screwgear sleeve 920 that is complementary to helical raceway 911 foraccommodating bearings 913. The inner surface of coaxial screw gearsleeve 920 also includes a machined tunnel for recirculation of bearings913 as the post 910 moves with respect to the sleeve 920. Therecirculating bearings are depicted as bearings 914 in FIG. 17B. Theouter surface of the enveloping coaxial screw gear sleeve also includesa helical raceway 921 for recirculating bearings 914 and an envelopingscrew gear 922. The worm 930 has a helical thread configured to engagethe enveloping screw gear 922 of the sleeve 920. The inner surface ofthe housing 940 has a helical raceway (not shown) that cooperates withhelical raceway 921 to retain bearings 914 and a tunnel forrecirculating bearings 914 as the coaxial screw gear sleeve 920 moveswith respect to the housing 940. Optionally, the coaxial screw gearsleeve 920 could have recirculating bearings both on the inside and theoutside of the sleeve and the recirculation tunnel could be between theinside and the outside of the sleeve, facilitating assembly andmanufacturing.

To expand the device 900, the worm 930 is rotated clockwise to engagethe enveloping screw gear 922 to rotate and translate the envelopingcoaxial screw gear sleeve 920 out of the housing 940. Thissimultaneously causes the post 910 to translate (but not rotate) out ofthe enveloping coaxial screw gear sleeve 920 and away from the housing940. Bearings 913, 914 enable the rotation of the enveloping coaxialscrew gear sleeve 920 with very little friction, enabling the device 900to exhibit a very high mechanical advantage and displacement controlwith very high resolution. The use of the enveloping screw gear 922enables the interface between the worm 930 and the enveloping coaxialscrew gear sleeve 920 to carry substantially higher loading.

Referring now to FIGS. 18A-18D, there can be seen another distractibledevice 1000 utilizing a coaxial screw gear sleeve according to anembodiment of the present invention. Device 1000 includes an envelopingcoaxial screw gear 1010, a housing 1020 and a worm 1030. The outersurface of enveloping coaxial screw gear sleeve 1010 includes a helicalgroove having a series of enveloping coaxial screw gear teeth 1014. Thehelical groove can cooperate with an internal thread 1021 on the innersurface 1022 of housing 1020 to allow the device 1000 to carry an axialload. In another embodiment, the gear teeth 1014 can be machineddirectly into the outer surface of the enveloping coaxial screw gearsleeve 1010. In one embodiment, the outer surface of the envelopingcoaxial screw gear sleeve 1010 can be a smooth machined surface thatacts like a bearing surface when configured with a similar smoothbearing surface on the inner surface 1022 of housing 1020 to enable thedevice 1000 to carry a lateral load.

To expand the device 1000, the worm 1030 is rotated to engage theenveloping coaxial screw gear teeth 1014 to rotate and translate theenveloping coaxial screw gear sleeve 1010 with respect to the housing1020. In one embodiment, the inner surface 1010 and center bore 1012 canbe configured to contain a post similar to the post 910 described inFIGS. 17A and 17B to compound the distraction of the device. In oneembodiment, no thread 1021 is present on the inner surface 1022 ofhousing 1020, so the helical groove and/or gear teeth 1014 of theenveloping coxial screw gear sleeve 1010 cause the sleeve 1010 totranslate with respect to the housing 1030 as the sleeve 1010 rotates.In such a configuration, the worm 1030 would carry any axial load,unassisted by an inclined interface between the enveloping coaxial screwgear sleeve 1010 and the housing 1020.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the present invention. It should beappreciated, moreover, that the various features of the embodiments thathave been described may be combined in various ways to produce numerousadditional embodiments. Moreover, while various materials, dimensions,shapes, implantation locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

1-26. (canceled)
 27. An expandable medical device, comprising: a firstouter member; a second outer member; and at least one coaxial screw gearsleeve mechanism disposed between the first outer member and the secondouter member, the coaxial screw gear sleeve mechanism including: athreaded post projecting inwardly from one of the first outer member andthe second outer member; and a corresponding sleeve having a threadedinterior surface surrounding and mating with the threaded post and ahelically geared exterior surface, wherein selective rotation of thesleeve causes an expansion of the first outer member with respect to thesecond outer member due to a telescoping expansion resulting from thesleeve translating relative to one of the first outer member and thesecond outer member simultaneously with the threaded post translatingrelative to the sleeve.
 28. The expandable medical device of claim 27,further comprising a drive mechanism having a drive thread thatinterfaces with the helically geared exterior surface of the sleeve suchthat rotation of the drive mechanism causes rotation of the sleeve. 29.The expandable medical device of claim 28, wherein there are a pair ofcoaxial screw gear sleeve mechanisms disposed between the first outermember and the second outer member driven by the drive mechanism. 30.The expandable medical device of claim 29, wherein the drive mechanismis a worm drive having a pair of separate threaded sections, eachthreaded section configured to interface with one of the coaxial screwgear sleeve mechanisms.
 31. The expandable medical device of claim 29,wherein the drive mechanism is capable of independently rotating each ofthe coaxial screw gear sleeve mechanisms to provide for differentialexpansion of the pair of coaxial screw gear sleeve mechanisms.
 32. Theexpandable medical device of claim 28, wherein the drive mechanism istranslationally stationary as the drive mechanism is rotated to drivethe helically geared exterior surface of the sleeve.
 33. The expandablemedical device of claim 27, wherein the sleeve fits within a sleeveopening in one of the first outer member or the second outer member suchthat the helically geared exterior surface of the sleeve interfaces witha corresponding internal thread in the sleeve opening.
 34. Asize-adjustable medical device, comprising: a first outer member; asecond outer member; a coaxial screw gear sleeve mechanism disposedbetween the first member and the second member, the coaxial screw gearsleeve mechanism including a sleeve having a helical thread with aplurality of gear teeth thereon; and wherein selective rotation of thesleeve causes an expansion of the first outer member relative to thesecond outer member due to a telescoping expansion of the sleevetranslating relative to one of the first outer member and the secondouter member simultaneously with the other of the first outer member andthe second outer member translating relative to the sleeve.
 35. Thesize-adjustable medical device of claim 34, further comprising a drivemechanism having a drive thread that interfaces with the helicallygeared exterior surface of the sleeve such that rotation of the drivemechanism causes rotation of the sleeve.
 36. The size-adjustable medicaldevice of claim 35, wherein there are a pair of coaxial screw gearsleeve mechanisms disposed between the first outer member and the secondouter member driven by the drive mechanism.
 37. The size-adjustablemedical device of claim 36, wherein the drive mechanism is a worm drivehaving a pair of separate threaded sections, each threaded sectionconfigured to interface with one of the coaxial screw gear sleevemechanisms.
 38. The size-adjustable medical device of claim 36, whereinthe drive mechanism is capable of independently rotating each of thecoaxial screw gear sleeve mechanisms to provide for differentialexpansion of the pair of coaxial screw gear sleeve mechanisms.
 39. Thesize-adjustable medical device of claim 35, wherein the drive mechanismis translationally stationary as the drive mechanism is rotated to drivethe helically geared exterior surface of the sleeve.
 40. Thesize-adjustable medical device of claim 34, wherein the sleeve fitswithin a sleeve opening in one of the first outer member or the secondouter member such that the helically geared exterior surface of thesleeve interfaces with a corresponding internal thread in the sleeveopening.
 41. A size-adjustable medical device, comprising: a firstmember; a second member; and a size-adjustable support engaging thefirst and second members to provide an adjustable separation distancebetween the first and second members, the support comprisingcommonly-actuated, coaxial first and second axially rotatable joints toprovide the adjustable separation distance, wherein the supportcomprises a first sleeve member and a second sleeve member eachincluding a helical external thread including a plurality ofsuperimposed teeth and an internal thread, wherein the first sleevemember is rotationally mounted in a first threaded lumen within thefirst member and the second sleeve member is rotationally mounted in asecond, substantially parallel threaded lumen within the first member,and wherein actuating the first and second axially rotatable jointsexpands the implant into an expanded configuration.
 42. Thesize-adjustable medical device of claim 41, further comprising a wormdrive having a threaded section configured to interface with the helicalexternal threads of the first sleeve member and the second sleevemember, wherein rotation of the worm drive rotates the sleeve members toactuate the first and second axially rotatable joints.
 43. Thesize-adjustable medical device of claim 42, wherein the worm drive has apair of separate threaded sections, each threaded section configured tointerface with one of the sleeve members.
 44. The size-adjustablemedical device of claim 42, wherein the worm drive is capable ofindependently rotating each of the sleeve members to provide fordifferential actuation of the first and second axially rotatable joints.45. The size-adjustable medical device of claim 42, wherein the wormdrive is translationally stationary as it is rotated to rotate thesleeve members.